1. Field of the Invention
This invention relates to aqueous solutions of perhalogenated compounds and more especially, but not exclusively, to perfluorinated compounds.
2. Brief Description of the Prior Art
Perhalogenated, for example perfluorinated, compounds are commonly used as surfactants in aqueous systems. Such compounds are, however, often not very readily soluble in water and are often available commercially in solution in a mixture of water and a polar organic solvent for example isopropanol or methanol.
There are problems associated with the use of such solutions of perhalogenated surfactants in certain applications. Such surfactants have been included in strongly acidic solutions for example in solutions of strong mineral acids, for example to improve wetting in acid etching processes in the electronics industry or to suppress mist formation in acid electroplating baths. The term strong mineral acid is used to indicate an inorganic acid giving a pH value, in 0.1 Normal aqueous solution, of less than 1.5. Such acids include hydrochloric acid, nitric acid and sulphuric acid. It may also be desired to include perhalogenated solvents in aqueous solutions of strong organic acid, for example acetic acid or formic acid, or in aqueous solutions of peroxy compounds species such as, for example, peracetic acid, perpropionic acid, permonosulphuric acid or hydrogen peroxide Strongly acidic media tend to cause at least some decomposition of the polar organic solvent component of the solution of the perhalogenated compound leading to contamination which can be particularly deleterious in, for example, the electronics industry where the degree of precision is such that even the slightest contamination may cause the production of a faulty end-product. Peroxy compounds can also react with solvents such as the lower alcohols to cause undesired contamination of reaction media, for example photoresist stripping or semiconductor wafer cleaning solutions for use in the electronics industry.
According to the present invention an alternative solvent system is provided for perhalogenated compounds which avoids or alleviates the above disadvantages. There are also provided media including perhalogenated compounds in the said solvent system.